1. Field of the Invention
The present invention relates to a micro-electromagnet, or an electromagnetic actuator. It more particularly applies to the fabrication of such an actuator by using technologies derived from those used for the fabrication of integrated circuits.
2. Discussion of the Related Art
In electromagnetic actuators, the generation of a magnetic field with a coil causes the displacement of an element sensitive to this field. Electromagnetic actuators especially apply to electrical relays, displacement sensors, electrovalves, and so on.
In the case of an electrovalve, the actuator is used to open or to close the passageway of a fluid inside a valve body. In miniaturized applications to which the invention relates, actuators generally act on a deformable diaphragm constituting a flap which is displaced by the actuator to close or to open a seat defining a passageway for the fluid and formed, for example, in a silicon plate.
Electromagnetic microvalves are particularly advantageous as compared with other types (electrostatic, piezoelectrical, thermo-fluid, opto-fluid or thermo-mechanical) of microvalves, because they provide a maximum of useful performances for a microvalve, namely the deformation ability of its diaphragm, the power of its actuator, its low electrical consumption, its supply voltage requirement, its response delay.
However, electromagnetic microvalves are very complex to fabricate because of the presence of an electromagnet and, in the prior art, have never been fully incorporated in integrated systems.
FIGS. 1A and 1B represent an example of a conventional electromagnetic microvalve whose valve body is formed by using the integrated circuit technology. FIG. 1A is a cross-sectional view of the microvalve. FIG. 1B is a partial top view of the valve body. The section plane of FIG. 1A is indicated by a dotted line A-A' in FIG. 1B.
Electromagnetic microvalves conventionally comprise a valve body 1, defining passageways for a fluid, and an electromagnetic actuator 2 combined with a diaphragm 3 for obturating one or more of the passageways.
The valve body 1 is formed from an etched plate, for example made of silicon, in order to define two transverse passages, an input 4 and an output 5, respectively, for the fluid. An annular seat 6, for cooperating with the diaphragm 3, is also formed in the silicon plate about an aperture 5' of the output passageway 5 which leads substantially in the middle of the circular diaphragm. The diaphragm 3 lies on a peripheral ring 7 protruding over the surface of the valve body which faces the diaphragm.
The electromagnetic actuator 2 is disposed over the achieved valve body, once diaphragm 3 is positioned. A ring 8 receiving a coil 9 is, for example, glued to the valve body 1. In the given example, ring 8 has an internal threading 10 adapted to cooperate with the external thread 11 of the solenoid constituting coil 9. The lower end of the coil lies on the diaphragm 3, over ring 7 which receives the periphery of the diaphragm. The diaphragm 3 is thus seal-pinched between the ring 7 and the coil 9.
A permanent magnet, in this case a cylindrical bar 12 made of a permanent magnetization material, is loosely disposed in the center of coil 9. The magnet 12 constitutes a movable element adapted to be axially displaced by coil 9.
When a current flows through coil 9, the magnetic field generated inside the coil causes bar 12 to slide down, which moves the diaphragm 3 to make it rest on seat 6. The valve is then closed, which blocks the flow of the fluid from the input passageway 4 up to the output passageway 5. To open the valve, it is generally sufficient to cancel the magnetic field by canceling the biasing of coil 9 so that the pressure on the diaphragm, of the fluid incoming in the valve, allows the communication with the output passageway 5.
A drawback of conventional electromagnetic microvalves is that their fabrication is complex because the coil and the permanent magnet are not integrated but are discrete elements that are added on the valve body. In addition, this method does not allow the implementation of a complete batch manufacturing such as the one used to make the valve body.